Characterization and Prevalence of a Polymorphism in the 3′ Untranslated Region of Cytochrome P4501A1 in Cancer-Prone Atlantic Tomcod

Atlantic tomcod ( Microgadus tomcod) from the cancer-prone Hudson River population exhibit a genetic polymorphism in the cytochrome P4501A (CYP1A) gene which is evidenced in Northern blot analyses by a truncated transcript and in Southern blot analyses by a deletion in the variant allele. To initially evaluate the functional significance of this polymorphism, we sought to characterize the molecular basis for this polymorphism and to determine its frequency in tomcod from other populations in which the prevalence of neoplasia is low. The common CYP1A allelic sequence was determined from β-naphthoflavone-induced tomcod cDNA and from tomcod genomic DNA. A sequence of the variant CYP1A allele was obtained by direct sequence analysis of the amplicons of variant tomcod cDNA and genomic DNA. CYP1A exon and intron structure is highly conserved between tomcod and all other teleost and mammalian species compared. Similarity of the deduced tomcod, rainbow trout, and plaice amino acid sequences was 72%, whereas similarity between tomcod and mammalian sequences was approximately 50%. The variant tomcod CYP1A allele results from a 606-bp deletion in the 7th exon of the 3′ untranslated region (UTR) of the cDNA. Polymerase chain reaction and Northern blot analyses revealed an absence of this CYP1A polymorphism in tomcod from other rivers. Studies in humans suggest that variation in CYP1A1 cDNA may impact on genetic susceptibility to environmentally induced neoplasia. Furthermore, studies in in vitro mammalian models indicate the importance of 3′ UTRs on gene expression by impacting on the stability of transcript. These results suggest that the 3′ UTR CYP1A polymorphism in tomcod may have consequences for the genetic susceptibility of Hudson River fish to hepatic neoplasia.